The conventional open wrench generally includes a driving head connected to a handle. In order to save material required, the driving head of the open wrench is designed to have grooves so as to reduce the material. A known open wrench is disclosed in U.S. Pat. No. 463,137 and has two driving heads on two ends of the handle and each driving head has grooves so as to reduce the material required. However, the top surface is parallel to the bottom surface of the driving head is even and the thickness from the top surface to the bottom surface is fixed. This cannot save too much material.
The present invention intends to provide a driving head for an open wrench to reduce material required.